This invention is related to computer controlled automatic transmissions. More particularly, the invention is concerned with a method used to determine the propriety of operating the transmission in what is known in the art of transmission controls as `hot mode`.
During certain vehicle operating conditions, transmission fluid temperatures can reach and exceed undesirable levels leading to fluid degradation and performance deterioration. In such situations, it is desirable and well known to take steps to prevent excessive temperatures by providing a hot mode of operation wherein various control actions are taken to decrease heat sources and/or improve heat dissipation. Generally, this involves application of the torque converter clutch to eliminate the major heat source, that being the characteristic losses of fluid coupling, and/or extending the shift points thereby increasing engine rpm and proportionally increasing transmission fluid flow through the transmission including the cooler lines.
Typically, entry into a hot mode is triggered by the transmission fluid temperature exceeding a predetermined threshold. The threshold is a compromise among many factors including undesirable peak fluid temperatures with high threshold calibrations, frequent and/or lengthy hot mode duration with low threshold calibrations, and mode cycling busyness.